FIGURE 1.

Schematic representation of the pulsed gradient spin echo (PGSE) diffusion sequence and water spins behavior. The classical PGSE sequence consists in the application of an initial 90° radiofrequency (RF) pulse and a refocusing 180° RF pulse. When interested in probing the diffusion behavior of water molecules, two diffusion gradient pulses are applied. These are characterized by amplitude (|G|), duration (δ) and time between their application (Δ). The diffusion gradients tag the spins of moving water molecules. This means that, those spins that move along the direction of the applied q-vector will elicit a signal reduction since they will have lost their coherence. The free induction decay signal is then acquired at echo time. Reprinted by permission from Macmillan Publishers Ltd (Patterson et al., 2008).